The present invention relates to the field of semiconductor manufacture, and more specifically to a boat for holding semiconductor packages during cleaning.
Semiconductor packages pass through a series of process steps and associated equipment during manufacturing. In order to maintain the integrity of the semiconductor packages, care must be used when handling and moving the semiconductor packages through each step in the manufacturing process and when transferring the semiconductor packages from manufacturing-related processes to shipping or distribution processes.
One aspect of semiconductor manufacturing involves a flux process, wherein solder connections are formed to join a semiconductor device to a support substrate and a device substrate package interconnection to an organic board. For example, the flux process can be implemented by heating a semiconductor assembly to solder temperature in the presence of solder flux. This will result in the formation of a solder bond. After heating, the semiconductor package is generally subject to a cooling cycle so that the solder hardens and the component parts are joined.
Through this heating and cooling process, residual flux deposits are formed on the exposed surfaces of the semiconductor package. In order to prevent semiconductor malfunction and to ensure proper package encapsulation, after completing the chip joining and other soldering processes during semiconductor package production, it is important that unwanted flux residue is removed from the semiconductor surfaces before subsequent assembly or shipping operations. This is accomplished by subjecting the semiconductor package to a cleaning operation.
Cleaning may also be necessary at other processing stages, such as when preparing surfaces for later processing, for removing other contaminants and debris, or for preparing a package before repair.
The cleaning operation used is generally determined by several factors. One factor is the process employed to assemble the semiconductor package. For example, a common cleaning operation involves the use of in-line cleaners that allow semiconductor packages to move uninterrupted directly from an assembly step, such as the flux process, to a cleaning step. This can be accomplished through automated mechanisms, such as robotics, which reduce or eliminate human intervention in the transfer process. In the alternative, it is possible to use centrifugal cleaners in order to remove flux residue and other contaminants from semiconductor packages.
Another factor affecting the choice of cleaning operation is the nature of the semiconductor package. In the case of packages with ball grid arrays, the cleaning operation selected is dictated in part by an interest in protecting the structure of the array. In particular, the packages must be cleaned and handled in a manner that prevents terminal balls on the package from coming into contact with any object that could dent, crush or otherwise damage them. The importance of ball grid array package handling is highlighted by the fact that the ball terminals have a low impact tolerance; they can be damaged with very little contact from other objects.
One way of protecting the semiconductor package during cleaning and associated handling is to place the package in a carrying device, such as a tray, cassette or boat, that is suitable both for the specific type of semiconductor package subject to cleaning and for the specific cleaner being employed.
Carrying devices typically have pockets that hold the semiconductor package. There may be one or more pockets in the carrying device. These carrying devices, alone or together with other carrying devices, may be placed directly in a cleaning apparatus or may be placed in a larger holding device, such as a tray holder, that is then placed in the cleaner.
The carrying devices conventionally available for cleaning ball grid array packages have been configured for use with in-line cleaners, which are common cleaning mechanisms used with ball grid arrays, particularly ceramic ball grid arrays. These carrying devices consist of a lidless, open-faced plate with pockets that are used to hold semiconductor packages.
Semiconductor package damage during cleaning and associated handling reflects the operating characteristics of in-line cleaners. For example, the cleaning function may cause horizontal semiconductor package movement within the carrying device that could scratch or dent the package, including ball terminals. Thus, the carrying devices that are used with these machines have support and containing features that are predominately focused on protecting the semiconductor packages from the kind of damage-causing behavior most commonly associated with in-line cleaners.
Currently, the same carrying devices used for in-line cleaners are also used in centrifugal cleaners, including the centrifugal cleaning systems made by Accel Corporation of Plano, Tex. However, due to the spinning mechanism inherent to centrifugal cleaners and the containment design of the in-line cleaner carrying devices, semiconductor packages often fly out of these carrying devices during cleaning and are subject to increased lateral and horizontal movement. To the extent that the semiconductor packages stay in the carrying devices normally used for in-line cleaners, the increased movement exposes the ball grid arrays on the bottom of the packages to increased damage potential by causing them to come into contact with other objects, including the bottom or sides of the carrying device.
Ball grad array packages continue to be popular due to their many benefits. For example, because of their small size, ball grid array packages offer significant savings in board real estate. Ball grid array packages also offer superior electrical performance because their shorter wirebond lengths help reduce inductance. Moreover, the solder ball pitch on a ball grid array package is very manageable during board assembly. Because of these and other positive features, new ball grid array packages are constantly being developed and demand for carrying devices and cleaning methods for these packages will continue to grow.
There exists a need for a carrying device, such as a boat, that will prevent semiconductor packages from falling out of the device during cleaning and that will hold semiconductor packages in place during cleaning in a manner that prevents damage to the packages.
There also exists a need for a method of cleaning semiconductor packages that will prevent the packages from falling out of a carrying device, such as a boat, during cleaning and that will allow the semiconductor packages to be held in place during cleaning so that the packages do not come into damaging contact with other objects.
These and other needs are met by the present invention, which provides a boat for semiconductor packages having a bottom plate with one or more receptacles for receiving semiconductor packages and a top plate having one or more through holes. Each through hole is smaller than the receptacle with which it corresponds in the bottom plate. An alignment mechanism ensures that the top plate is aligned with the bottom plate in a manner that results in each through hole being positioned directly over a respective one of the receptacles. An attachment mechanism releasably attaches the top plate to the bottom plate in a co-planar relationship that results in the formation of a vertical space between the two plates.
One of the advantages of the present invention is the prevention of movement by a package in a vertical direction during cleaning. This allows the boat to be used in both in-line cleaners and centrifugal cleaners.
The present invention also advantageously prevents packages from extending through the hole in the bottom of a receptacle. This permits the boat to be used with ball grid array packages because ball terminals on the underside of the package are protected from impact and damage during cleaning and associated handling.
Another aspect of the present invention provides a method for cleaning semiconductor packages. The method includes the steps of placing a semiconductor package in a receptacle in the bottom plate of a boat and securing the package in the boat by attaching the top plate over the bottom plate in an aligned position so that the through holes in the top plate correspond with the receptacles in the bottom plate.
Other advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description. The embodiments shown and described provide illustration of the best mode contemplated for carrying out the invention. The invention is capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings are to be regarded as illustrative in nature, and not as restrictive.